The present invention concerns a voltage converter as set forth in the classifying portion of claim 1.
Such voltage converters, of the blocking or reverse converter type, also known as so-called xe2x80x9cflybackxe2x80x9d converters, belong to a switching power supply topology which, besides a central inductor, preferably with two potential-separated windings, has a switch on the primary side, which is switched for controlledly connecting the inductor to an input voltage source, and on the secondary side, an output capacitor connected to the inductor by way of a diode.
A circuit topology of that kind, which is generally known as such and which is disclosed for example in Schott, xe2x80x9cPower-Factor-Controller . . . xe2x80x9d, Components 31 (1993), issue 2, pages 46 ff, has, as a converter principle, numerous advantages which make the circuit arrangement highly suitable for the implementation of switching power supplies: thus, when that principle is adopted, it is possible in particular to control and limit the switch-on current, and the output voltage can be greater or smaller than the instantaneous input voltage so that any output voltages can be generated from the input voltage. A further advantage of that topology is in addition the galvanic separation of the primary and the secondary sides if a transformer is used as the inductor.
Nonetheless such a voltage converter circuit of the general kind set forth, of the flyback converter type, also suffers from disadvantages inherent therein by virtue of the principle involved, thus for example the heavy loading of the output diode due to high currents, with a correspondingly disadvantageous consequence for the level of efficiency of the circuit (due to the fixed reverse voltage of the diode) and a relatively severe dependency of the output voltage on the output current.
There is therefore a need to improve the effectiveness or efficiency of such a converter circuit of the general kind set forth, so that the object of the present invention is to provide a voltage converter of the general kind set forth, of the flyback converter type, which is improved in terms of its efficiency, in particular in regard to minimizing secondary-side losses, and the dependency of the output voltage on the load current.
In an advantageous manner in accordance with the invention, the blocking element on the secondary side is in the form of a switching element, in particular a transistor, which, due to the control signal according to the inventionxe2x80x94like the blocking characteristic of the diode of the general kind set forthxe2x80x94alternately blocks and conducts in dependence on the conduction condition on the primary side so that, to produce the flyback converter effect, at no point is there an unwanted common switch-on condition between input and output terminals on the primary and secondary sides, which would result in uncontrolled and unwanted over-currents.
In this respect, in accordance with the present invention, a particular difficulty involves compensating for the delays which are caused by parasitic capacitances or the like upon actuation of the switching element, by nonetheless achieving a clear and tidy switching characteristic. In accordance with the invention that is achieved in that the control means according to the invention cause the control signal for producing the blocking condition to lead the primary-side clock by a short time interval, in which respect it has proven to be particularly suitable for triggering for that leading control signal also to be effected on the primary side, more specifically in particular by means of the actuation unit which also provides for pulse width-modulated actuation of the primary-side switching element.
Advantageous developments of the invention are set forth in the appendant claims.
Thus, in the practical circuitry implementation, both the primary-side switching element and also the (secondary-side) further switching element is implemented in the form of an FET-transistor with purely ohmic path or channel resistance in the conducting condition, in which respect here suitable, commercially available, integrated circuit components provide for the pulse width-modulated, preferably load-regulated actuation of the primary-side field effect transistor.
In this respect, in accordance with the invention, preferably a further signal output of the integrated component, which is of a ramp configuration in the primary-side clock phase, is used in order for example by means of a Schmitt trigger function to obtain the leading control signal for the secondary-side further switching element.
In that respect, in accordance with a further preferred development, it can in particular also be advantageous for that control signal to be transmitted by means of a suitable transformer, optocoupler or the like in galvanically isolated relationship from the primary side to the secondary side.